The present invention relates to an inter-module interface circuit within a semiconductor device or between a semiconductor device and an external circuit, and an interface circuit between different types of power source voltages of a semiconductor device operated by two or more power source voltages.
A pull-up circuit improves a margin of an input voltage level by fixing an input terminal to a desired level.
FIG. 1 illustrates a configuration of a bus-hold circuit, which is a typical pull-up circuit.
First, focusing on FIG. 1(a), an inverter 11 is inserted between an input terminal IN and an output terminal OUT. An output of the inverter 11 is branched and subsequently input to a MOSFET. If a first MOSFET 12 is a pMOSFET, the first MOSFET 12 is turned on when an “L” level voltage is applied. Here, the first MOSFET 12 is not limited to a pMOSFET and an nMOSFET can also be used.
If an “H” level voltage is applied to a gate terminal when the first MOSFET 12 is an nMOSFET (or, alternatively, if an “L” level voltage is applied when the first MOSFET 12 is a pMOSFET), the first MOSFET 12 is turned on.
An invention described in Japanese Patent Laid-Open No. 2008-21733 discloses a technology that enables high-speed operation by optimizing the thickness of a gate oxidation film when there is a circuit module using a plurality of power source voltages in a single semiconductor integrated circuit. When considering the thickness of a gate oxidation film, a bus-hold circuit of FIG. 1(a) is transformed such as shown in FIG. 1(b). That is, a input voltage-adjusting MOSFET 21 is inserted between the input terminal IN and the inverter 11. The “H” level of a signal input to the input terminal IN is lowered by a threshold voltage Vth of the input voltage-adjusting MOSFET 21 (Vcc−Vth), and thereby input potentials of the input terminal IN and the inverter 11 are separated to protect the gate oxide film of the internal circuit.
It is also conceivable, as shown in FIG. 1(c), to insert a NOR gate 31 instead of the inverter 11 to provide a control terminal CNT as an input terminal. This has an advantage that an output terminal OUT can be fixed regardless of the level of the input terminal IN by setting the control terminal CNT to “L”.